The research outlined in this Administrative Supplement to Grant R01 AI094599 involves an ongoing collaboration between Min Lu (Rutgers New Jersey Medical School) and Daniel Malamud (New York University College of Dentistry). Due to power failure during Hurricane Sandy, we lost all stable Chinese hamster ovary (CHO) cell lines expressing SRCR1 module fragments of the human scavenger receptor gp340, polyclonal antibodies raised in rabbits against a synthetic peptide derived from the SRCR1 module, and gp340 peptide and protein entry inhibitors. The supplemental funds are requested to reproduce these critical and proprietary research materials and reagents and to define the molecular target and mechanism of action of soluble gp340- based anti-HIV-1 agents. These studies could lead to discovery of novel entry inhibitors that target early infection to prevent mucosal HIV-1 transmission. Experiment 1: To generate stable CHO cell lines for high-level production of secreted SRCR1 module fragments. Experiment 2: To characterize the structural properties of the SRCR1 domain both free and bound to the V3 region of HIV-1 gp120. Our overall goal is to elucidate how HIV-1 envelope glycoprotein function in cell entry is modulated through the gp340-gp120 interaction; to use this knowledge to optimize SRCR1 entry inhibitors for antiviral potency; and to test these hypotheses in a humanized mouse vaginal transmission model, in collaboration with Dr. J. Victor Garcia-Martinez (University of North Carolina School of Medicine) in years 4 and 5. To achieve this goal, we will express and purify large quantities of recombinant gp340 fragments in CHO cells, and carry out a combined structural and physicochemical investigation of the SRCR1 domain in complex with the V3 region. These experiments will enable us to develop optimized SRCR1 entry inhibitors for evaluating their effectiveness to protect against mucosal HIV-1 infection in vivo. Fulfilling the central objective of the parent grant would not be possible without the with-cost extension of support that would significantly mitigate the impact of Sandy on this research project.